According to this latest tutorial from NETTUTS.com, you should be using PHP's PDO database access layer to interact with your database of choice.

Many PHP programmers learned how to access databases by using either the mysql or mysqli extensions. Since PHP 5.1, there's been a better way. PHP Data Objects (PDO) provide methods for prepared statements and working with objects that will make you far more productive!

The introduce what PDO is, what kind of databases it supports and, of course, some code to get you started in connecting your application to the backend. They show how to handle exceptions, how to use placeholders, and performing inserts and selects on your data.